Backflow guide for turbine starter



9 as. SIEGLER ET 3,474,622

BACKFLOW GUIDE FOR TURBINE STARTER Filed Sept. 18, 1967 INVENTORS3085197 4. E/A/SA 5w ,eoaser s. 5/561 52 United States Patent O3,474,622 BACKFLOW GUIDE FOR TURBINE STARTER Robert S. Siegler,Calabasas, and Robert L. Binsley, Sepulveda, Calif., assignors to NorthAmerican Rockwell Corporation, a corporation of Delaware Filed Sept. 18,1967, Ser. No. 668,549 Int. Cl. F02g 3/00; F02c 3/00; F02k 1/00 U.S. Cl.6039.77 6 Claims ABSTRACT OF THE DISCLOSURE A pulse jet-type combustorfor discharging combustion product through a plurality of tubes to starta turbine. Adjacent the exit side of the turbine is a backfiow guidethat promotes superior flow characteristics of the backflowing air beinginducted through the turbine rotor into the combustor between successivecombustion strokes. The guide allows enhanced precompression to beachieved to increase combustion efliciency.

BACKGROUND OF THE INVENTION The instant invention relates to a powersystem Ior starting self-sustaining engines and more specificallyconcerns a pulse jet combustor whose hot gases are discharged into theinlet side of a starter turbine. The output motion of the turbine iscoupled to the self-sustaining engine being started.

The broad concept of positioning the exhaust portion of a pulse jet-typecombustor in operative driving relationship with a turbine is known inthe art. Such a power generating arrangement used as a supercharger fora vehicle internal combustion engine is disclosed in U.S. Patent No.2,963,863 to Middlebrooks.

It is also known in the art to use the hot gases generated in acombustor, not of the pulse jet-type, for operating a turbine designedto start, i.e., initiate motion of, an engine system (e.g., U.S. PatentNo. 3,004,387 to Woodward).

As disclosed in co-pending U.S. applications, Ser. No. 576,726, filedSept. 1, 1966, now Patent No. 3,411,292, and Ser. No. 583,624, filedOct. 3, 1966, now abandoned (which applications are assigned to theassignee of this invention) the combustion product of a resonating orpulse jet-type combustor may be discharged through a plurality ofexhaust tubes to the inlet side of a starter turbine designed to start aself-sustaining engine. This invention is an improvement over thecombustors disclosed in these applications and is primarly aimed atincreasing the combustion efiiciency by a backfiow guide that promotessuperior flow characteristics of the charge of ambient air that isautomatically inducted through turbine rotor and the combustor tubes andinto the combustion chamber between successive combustion strokes.

SUMMARY OF THE INVENTION Briefly described, the instant inventioncontemplates an accessory incorporated in a power system characterizedby a pulse jet or resonating type combustor which discharges gases tothe inlet side of an adjacent starter turbine. The accessory is abackflow guide positioned adjacent the exit side of the turbine. It iswell-known that between successive pulses of combustion in the pulsejet-type combustor the internal pressure of the combustor diminishes toa value below the ambient pressure with the result that a new charge ofambient air is inducted through the turbine and into the combustor. Theoccurrence is commonly referred to as the backflow stroke or phase ofthe overall power cycle.

The backfiow guide has a guideplate that encircles the turbine anddiverges rearwardly, i.e., in the direction in which the hot gases areto be ejected, from the exit side of the turbine. In addition itsinterior periphery may be slightly convex. Between successive combustionstrokes, the backfiowing air attaches to or flows along the surface ofthe guideplate and is smoothly guided through the passageways defined bythe turbine blades and introduced into the combustor. By eliminatingturbulent, erratic flow characteristics of the backflowing air, agreater mass of backflow air traveling at a greater velocity arrives inthe chamber for accomplishing enhanced precompression of the air. Thebackfiowing air and the charge of air being inducted through theconventional one-way flapper valves rarn together with an increasedforce to produce the greater precompression. This in turn accomplishessuperior combustion efliciency. In another aspect, the backflow guidehas a second guideplate concentric with the turbine and which convergesrearwardly from the exit side of the turbine. The second guide platefunctions to further augment the desired smooth flow characteristics ofthe backflowing air. The two guideplates define an annular passage witha funnel-shaped opening exposing the turbine blades. The plates may berigidly interconnected by a plurality of stiffening ribs.

The advantages and operation of the invention will be fully understoodupon studying the following detailed description in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view partiallyschematic and sectional, showing a pulse jet combustor adjacent astarter turbine with the backflow guide of this invention positionedadjacent the exit side of the turbine.

FIG. 2 is a perspective view of the backfiow guide showing its inner andouter guideplates and the annular passage defined therebetween thatexposes the turbine blades.

FIG. 3 is a schematic view showing the backflow guide with a singleguideplate integrally formed with a mounting plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will beexplained in conjunction with a combustor 10 of the resonating orpulse-jet type, shown in FIG. 1, that generates power for starting aturbine 14 suitably keyed to a power shaft (not shown). The specificdetails and mode of operation of combustor 10 are fully explained in thetwo previously referred to U.S. applications that are incorporated byreference. As disclosed in these applications, air is intermittentlyadmitted through a bank 20 of one-Way flapper valves and through a fuelinjector 24. Initially a predetermined suitable mixture of fuel and airprepared for combustion is introduced into combustion chamber 30 whereit is ignited by spark plug 32 to produce combustion product. Thecombustion product is propelled into and against dome 34 and eventuallyis discharged outwardly through a plurality of exhaust tubes 40, 42, 44,and 46. Exhaust tube 40 extends rearwardly from dome 34, is bent in aspiral configuration around the exterior of combustion chamber 30 andterminates in an exit opening 41 adjacent turbine 14. The other exhausttubes 42, 44, and 46 that are depicted schematically are arrangedsimilarly to exhaust tube 40. Combustion product being ejected throughthe exit openings of the exhaust tubes impinges against turbine blades16 to thereby, in the customary manner, impart rotation to turbine 14.Thus, the combustion product enters the turbine through inlet side 18and egresses through exit side 19.

The power output capacity and overall efiiciency of combustor 10 can bemarkedly improved by facilitating and increasing the back-flow ofambient air through turbine blades 16 and the exhaust tubes into thecombustion chamber. One of the prime functions of the backfiowing air isto ram and mix with the fresh charge of air being admitted through thebank 20 of flapper valves to achieve precompression of the air. Byintensifying the precompression value of the air prior to its combustionwith the fuel, a greater energy release and hence power capacity can beachieved.

The precompression that can be achieved is a function of the mass of thebackflowing air and to the lesser extent its velocity. The sharp edgesof the individual turbine blades which define the passageway throughwhich the combustion product and backflowing air intermittently pass,naturally inhibit the mass and volume of air that can be inductedbetween combustion strokes. The sharp edges tend to cause turbulencewhich significantly reduced the mass and velocity of the backi'lowingair causing a power loss. In addition the edges promote separation ofthe backfiowing air thereby failing to take ad vantage of the maximumspace of the flow passageways. These conditions that have heretoforeinhibited and impaired attaining maximum precompression are eliminatedby the instant invention.

Referring to FIGS. 1 and 2, there is shown a backflow guide 50 designedto greatly augment precompression. Backflow guide 50 includes an outerannular-shaped guideplate 52 which encircles turbine 14 and ispositioned a radial distance in the order of 0.030 inch from the outertips of turbine blades 16. The spacing is standard to assure minimalenergy loss with respect to the hot gases being exhausted. Plate 52diverges outwardly and rearwardly from turbine 14 in the direction inwhich the hot gases are to be ejected. Its inner periphery 53 is convexin the axial direction. The optimum convexity, to assure the desiredflow characteristics of the backflow air, is primarily dictated by theturbine diameter. By way of example, when the turbine diameter isapproximately 9 inches, the minimum optimum diameter for the curvatureof plate 52 has been found to be approximately 2% inches. Below theminimum optimum radius, the entering stream of backfiowing air tends toseparate from convex inner periphery 53. Other secondary factorsinfluencing the optimum curvature are: (l) The ratio of blade height topitch diameter, and (2) The exhaust gas temperature and velocity. Theaxial length of plate 52 terminates at a point beyond that zone of plate52 where the stream of backfiowing air first attaches to periphery 53.The curvature of plate 52 will always be described by an arc less than90. The desired arc, as best determined by experiment action, willgenerally be in range of between 50 and 75 The inner end of plate 52terminates in a radially outwardly extending flange 54 that is welded orotherwise suitably attached to mounting plate 55 which also serves tofix the relative positions of the exit openings of the exhaust tubes.Backflow guide 50 also includes an inner guideplate 60 whose inner end62 terminates adjacent and slightly downstream of the exit side 19 ofturbine 14. Guideplate 60 converges inwardly in a downstream directionand preferably terminates in the same plane in which the downstream endof plate 52 terminates. The inner periphery 63 is slightly convex in theaxial direction. A plurality of narrow stiffening ribs 68 interconnectplates 52 and 60 to fix their relative spatial relationship and supportthe overall backflow guide 50. Plates 52 and 60 define an annularpassage 65 which exposes blades 16 and allows communication between theamibent air and combustion chamber 30.

With the structural characteristics of backflow guide 50 now understood,its advantages and operation can be fully explained. Admission of thefuel-air mixture in combustion chamber 30 accompanied by ignition fromspark plug 32, produces an explosion that instantaneously generatescompression waves and a concomitant pressure increase. The increasedpressure in chamber 30 serves to close the flapper valves as thecombustion product is propagated through exhaust tubes 40 through 46 tobe eventually impinged against turbine blades 16. The combustion productin imparting rotation to turbine 14 is exhausted through exit side 19and annular passage 65. It should be noted that guideplates 52 and 60neither promote nor restrict the ejection of the combustion product,i.e., they do not function to influence the movement of the exhaustproduct either positively or negatively. After a predetermined lapse oftime the pressure within combustion chamber 30 decreases to a value lessthan ambient pressure at which time the flapper valves reopen to admit afresh charge of air. Simultaneously a charge of air is drawn intocombustion chamber 30 over backflow guide 50.

Backflow guide 50 promotes a smooth flow of ambient air through annularopening into the passageway defined by blades 16. Rather thanexperiencing irregular and turbulent flow, the charge of backflowing airattaches to the peripheries 53 and 63 of guideplates 52 and 60respectively and becomes relatively laminar. The air occupies themaximum volume of the passageways defined between blades 16 and hencethe overall charge of air being admitted into chamber 30 through theindividual exhaust tubes 40 through 46 is maximized. The charge ofbackflow air passing through the exhaust tubes 40 through 46 eventuallyenters combustion chamber 30, hammers into, and becomes mixed with thefresh charge of air admitted through the flapper valves. The two chargesof air approaching each other from opposite directions serve toprecompress the air and prepare it for the next combustion cycle. Atthis juncture the sparkplug 32 or other igniting source is no longerrequired and has been terminated. Reignition of the fuel-air mixture isaccomplished by the residual hot gas trapped between the two new chargesof air. Hence the power cycle of combustor 10 is self sustaining muchlike the operation of a conventional pulsejet.

It can now be seen that overall combustion efficiency is greatlyenhanced clue to the fact that backflow guide 50 greatly minimizes theturbulence and obstruction to the charge of backflowing air so that asmooth flow of air characterized by maximum mass can be drawn into thecombustion chamber to achieve a much enhanced precompression.

FIG. 3 depicts a backflow deflector 70 having only a single guideplate80, analogous to guideplate 52, shown in FIG. 2, integrally formed witha mounting plate 82. Formed through the center of guideplate 80 is acircular opening 84 having a diameter slightly larger than the diameterof the turbine. Guideplate 80 and outer guideplate 52 of the backflowguide 50, shown in FIG. 2, operate identically.

What is claimed is:

1. In a turbine starter device characterized by a pulsejet typecombustion chamber which alternately generates combustion products andinducts backflow air through a turbine positioned adjacent the exhaustportion of the combustion chamber, and means for conducting gas betweenthe combustion chamber and turbine, the improvement comprising:

a backflow guide extending rearwardly from the exit side of the turbineand having an end exposed to atmospheric air and diverging from theouter periphery of said turbine for improving the flow characteristicsof backflowing air to enhance precompression of air in the combustionchamber, said guide having an inner periphery over which backflow airpasses which is convex in axial direction.

2. The structure according to claim 1 wherein the backflow guide is acantilevered annular plate encircling the turbine that diverges awayfrom the exit side of the turbine.

3. The structure according to claim 2 wherein the interior periphery ofthe plate over which backflow air passes extends from 50 to of arc.

4. The structure according to claim 2 wherein the backfiow guide has asecond annular cantilevered plate spaced radially inwardly from saidfirst mentioned plate and being concentrically aligned with the turbine,said second plate converging away from the exit side of the turbine, thetwo plates defining an annular funnel-like passageway exposing theturbine blades to atmospheric air.

5. The structure according to claim 4 wherein the outer periphrey of thesecond plate over which backfiow air passes is convex in an axialdirection.

6. The structure according to claim 4 wherein the backflow guide furthercomprises a plurality of stiifening ribs interconnecting the two platesto fix their relative spatial relationship.

References Cited UNITED STATES PATENTS 6/1965 Melenric. 8/1966 Keen.

' CARLTON R. CROYLE, Primary Examiner US. Cl. X.R.

